**Core Concept**
Stellate ganglion block is a procedure that involves the injection of local anesthetic into the stellate ganglion, a collection of sympathetic nerve fibers located in the neck. This block can cause a range of physiological effects due to the disruption of sympathetic outflow from the ganglion.

**Why the Correct Answer is Right**
The correct answer is **D. Increased blood pressure**. This is because stellate ganglion block typically causes vasodilation and a decrease in blood pressure, due to the loss of sympathetic vasoconstrictor tone. The stellate ganglion is responsible for the sympathetic innervation of the upper limb and the head and neck, and its blockade leads to a decrease in peripheral vascular resistance, resulting in a drop in blood pressure.

**Why Each Wrong Option is Incorrect**
* **Option A:** Horner's syndrome is actually a sign of stellate ganglion block, characterized by miosis (pupil constriction), ptosis (eyelid drooping), and anhidrosis (absence of sweating) on the same side as the block.
* **Option B:** Bradycardia can occur as a result of stellate ganglion block, as the sympathetic nervous system normally helps to regulate heart rate. The loss of sympathetic tone can lead to a decrease in heart rate.
* **Option C:** Increased sweating on the face and upper limb is a sign of stellate ganglion block, not a decrease. The block leads to a loss of sympathetic tone, which normally inhibits sweating, resulting in an increase in sweating on the affected side.

**Clinical Pearl / High-Yield Fact**
Stellate ganglion block is used to treat a range of conditions, including Complex Regional Pain Syndrome (CRPS), hot flashes, and hypertension. It is also used to diagnose sympathetic nervous system disorders.

**Correct Answer: D. Increased blood pressure**